The physical process, by which the air containing oxygen is drawn into the lungs and air containing carbon dioxide is forced out from lungs is called breathing.
Breathing involves two steps, inhalation (inspiration) and exhalation (expiration).
Inhalation (Inspiration)
1. Ribs move upwardsand outwards.
2. Diaphragm is pushed downwards and flattens.
3. Volume of chest cavity increases.
4. Lungs expand, air pressure becomes low.
5. Atmospheric air at higher pressure rushes into the lungs
Exhalation (Expiration)
1. Ribs move downwards and inward.
2. Diaphragm moves upwards and becomes dome shaped.
3. Volume of chest cavity decreases.
4. Lung size reduces, air pressure becomes high.
5. Air rushes out of lungs as atmospheric air pressure is lower.
